The trees, bought from the Middle East, were used to decorate public monuments – most died for lack of soil and water.
Mayawati’s party has accused the new government of neglecting them, but denies any corruption.
Officials have not confirmed how many trees were bought or at what cost.
But reports suggest that each tree cost up to $460 (£290) and additional expenditure was incurred in transporting and planting them. Some accounts suggest as much as $10m may been spent on the trees.
Hundreds of these trees are lying in the Jiyamau area of the state capital, Lucknow.
Mayawati lost power in March, and since then the new chief minister, Akhilesh Yadav, has been talking of investigating alleged scams during her administration.
She has faced criticism for spending vast amounts of public money on numerous statues of elephants and herself in a state that has a high crime rate and poor health indicators.
A senior member of Mayawati’s Bahujan Samaj Party defended the purchase of the palm trees and denied any suggestion of corruption.